The invention concerns a method of controlling the commutation of an electronically commutated motor, and a motor for carrying out such a method.
In motors with electronic commutation, also referred to as ECMs, a variety of parameters and boundary conditions must be taken into account in the context of a commutation operation; this is not always easy. When a motor of this kind operates with a full bridge circuit, errors in commutation can result in a short circuit in the full bridge, which causes its destruction. If the commutation is controlled by a microcomputer, it is important for cost reasons to use an economical microcomputer, and it is then desirable to minimize the number of time measurements taking place concurrently.
It is therefore an object of the invention to make available a new method for controlling the commutation of an electronically commutated motor, and a new motor for carrying out such a method.
According to the present invention, this object is achieved by estimating how long it will take for the rotor to pass through a predetermined angle, detecting how long it actually takes, and regulating the communication in accordance with calculations made using these data. Here a predictive calculation, i.e. a kind of estimate based on available data, is made of a first time span that the rotor will need in order to pass through a specified rotation angle that lies between a first rotational position and a later second rotational position at which a switching operation is to be effected in the motor. Upon actual passage through the first rotational position, a reference time is identified and stored. The time difference between the present time and stored reference time is then calculated repeatedly and compared to the first time span; and if a specified relationship exists between the time difference and the first time span, the switching operation is performed. The result is that a variety of commutation operations can be optimally controlled using a timer that counts continuously, for example in the manner of a clock.
A very advantageous development of the invention is, when one stator winding current is switched off, to set an indicator about which current is the next current to be switched on. What is achieved thereby is that the motor, as it rotates, advances an indicator which indicates which steps are to be performed next. It can also be said that the rotational position at which the reference time is measured xe2x80x9cmigratesxe2x80x9d along with the rotation of the rotor, so that a new reference time is continually being re-determined, that time representing, so to speak, a fixed reference point, to which subsequent calculations can refer, for switching the current on and off in a phase.
Very advantageously, that reference point, i.e. the first rotational position, is defined in such a way that under all motor operating conditions, the second rotational position is reached later than the first rotational position. This results in a great deal of freedom in selecting the rotational positions at which, under the instantaneous operating conditions of the motor, a stator current is to be switched on or off. It is particularly advantageous in practice to use as the reference point, in each case, the Hall change before the previous one, as described below with reference to FIG. 33.